Method and apparatus for recovering chemicals of sulphate paper pulp



Jam-25, 1944. N A; LEWTHMTE 2,339,998

umaon fin APPARATUS FOR nmcovnnm summons 0F SULPHATE PAPER PULP Filed July 19. 1940 2 Sheets-Sheet 2 Patented Jan. 25, 1944 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR RECOVER- {ggPCHEMICALS OF SULPHATE PAPER Norman A. Lewthwaite, Port Townsend, Wash-.. assignor to Crown Zellerbach Corporation, San Francisco, Calil., a corporation of Nevada Application July 19, 1940, Serial No. 346,412 2 Claims. 210-499) My invention relates to soda, sulphate pulp, or up by the filter drum and separately collected similar processes for making wood pulp, in which and then the remaining portion of chemical soluthe chemicals used are costly, and from which, tion held by the sheet is washed out by the applitherefore, the recovery of as much as possible of cation thereto for a limited time of a weak liqthe reclaimable chemicals held by the pulp blown nor wash and the two filtrates so obtained are from the digester is exceedingly important. then mixed, a much higher density liquor is re Heretofore so-called "rotary vacuum filters" covered; and the cost of final evaporation of such have been generally used for the purpose of such liquor is greatly reduced.

recovery. As well known, such a filter comprises The further details of my invention are herea drum, the rim of which is covered with fine 1o inafter fully described with reference to the acwire cloth and the drum is rotated in a vat filled companying drawings:

with black liquor and pulp discharged from the In the drawings: digester. The interior of the drum of these Figure 1 shows a diagrammatic elevation of rotary filters is divided into a series of consecuthe digester and the auxiliary devices customarily tive, radially-disposed circumferential compartemployed in producing paper-making pulp from ments or trays, into which the liquor removed wood by the soda process;

from the sheet 01' pulp picked up by the drum Figure 2 shows a diagrammatic perspective of is drawn, and conveyed to a suitable receptacle. the apparatus employed by me for practicing my It is customary to apply a shower to the sheet for invention;

aiding in the washing out of the liquor held by Figure 3 shows a diagrammatic end-view of the the sheet. drum of my rotary vacuum filter;

The rotary vacuum filter has one poor feature, Figure 4 shows an end-view of the drum of my namely the large reduction in the solids content filter partly in section, and illustrates a specific of the liquor recovered, which reduction correconstruction of the interior of the drum which spondlngly increases the cost of evaporating the I found convenient to employ; and recovered chemical solution. To overcome such Figures 5 and 6 show details of construction. difllculty, these filters have been used in series, Referring first to Figure 1, a digester i empties with the hot-water shower applied to the sheet into a blow tank 2, from which the pulp is carof pulp carried on the drum of the last of the ried by a pipe-line 3 to a vat 4, in which is rotated series of filters, and the filtrate obtained from so a filtering vacuum drum 5. The rim of the drum the last filter, which is a weak" liquor, being is understood to be covered with a filtering meapplied as a shower to the sheet of pulp formed dium, for example, fine wire-cloth. The interior on the preceding filter; and, in similar manner of the drum is divided into an endless series of this procedure is carried on backward, through compartments for receiving the filtrates drawn the series, if composed of more than two units of from the sheet of pulp through the filtering rim.

said filters. Preferably the arrangement of such compart- Such arrangement effects decided improvement ments is as shown by 6 in Figure 4. These comin the concentration of the liquor recovered; but partments are connected to spoke-like pipes i, the disadvantage of the arrangement is that it having outlets 8 located around the hub of the requires several filters and thus a large capital drum. investment, as well as repumping between filters At one end of the drum 5 is provided a suction and the pumping of large volumes of filtrate. box 32 (Figs. 2, 5 and 6) having two arcuate vac- The purpose of my invention is to provide an uum chambers 33 and 34 E'lCIOSillg, respectively, improved method to effect an efficient recovery of the outlets 8 (Fig. 4) of the drum when registerthe chemicals with only a single rotary vacuum ing therewith during the rotation of the drum. filter, that is, to obtain the same concentration of The lower-level suction-pipe 9 connects with the solids content in the recovered liquor as obvacuum chamber 33 and the upper-level suctiontainable from the employment of a series of filpipe l0 connects with vacuum chamber 34. By ters, and in a more efiicient manner. By my inthis arrangement, as will appear, the filtration vention a substantial reduction in the high cost process carried on by the filter (Fig. 3) is divided of installation and also in the cost of operation intoa relatively large zone 20 discharging through of a series of said filter units is made possible. the vacuum chamber 33, for the removal of the I discovered by extensive tests that if the full full-strength high-density liquor held by the inistrength high-density black liquor is first retial section of the sheet. and a smaller one 2| moved from the initial portion of the sheet picked as discharging through the vacuum chamber 34 which serves for the removal of the remaining liquor from the sheet with the application of a shower, No vacuum is applied to the sheet while carried through the arcuate zone 3|.

The lower-level suction-pipe 9 leads to strong liquor chest I! (Figure l). The upper-level suction-pipe Iii is connected to a receptacle II. A vacuum is assumed to be maintained by suitable means (not shown) in the chambers 33 and 34 and in the suction pipes 9 and Ill, and the receptacle II, The described apparatus will be sufilciently understood by anyone practical in the art without giving further details thereof.

A shower i3 of weak liquor is applied to the sheet in the first zone 20. This shower, however, is located a predetermined distance from the boundary between zones 20 and 2| so that the weak liquor from this shower will not have time to penetrate entirely through the sheet before such showered sheet portion has reached the second zone 2|. The shower I3 is supplied through the medium of pump H from the receptacle ii containing the weak liquor filtrate obtained from the second zone 2|.

A second shower of hot water is sprayed on the pulp sheet in zone 2i by spray pipe 30. The excess weak liquor filtrate from receptacle l I passes through separator l and is finally intermixed with the strong liquor in chest I2. The air and vapor gases contained in receptacle H escape through pipe Ila to separator it which is connected with trap l1, and the latter is connected with vacuum chamber l8; and the apparatus is otherwise arranged in the customary manner, sufiiciently indicated in Figure 1, without further description.

The second and final shower of hot water 30 washes the weak-liquor" from the first shower i3 from the sheet and maintains the "weak liquor in receptacle II in proper consistency. The hot water shower 3!! must be controlled according to requirements.

The sheet of pulp l5, formed on the drum 5 is finally lifted from the latter by the customary doctor 22, and drops into a hopper 23 and is conveyed by conduit 24 to the vat 25 of a secondary rotary vacuum filter 26. The liquid here drawn from the pulp is discharged to the sewer because its chemical content is negligible.

The pulp, scraped oil the secondary filter 26' drops into a hopper 21, which discharges into the pulp chest,

Naturally the distances and locations of the showers and boundaries of the vacuum zones 20 and 2| are not absolute, and should be changed for different speed of rotation of the drum, dinerent thicknesses and characteristics of the pulp sheet, etc., in order to produce most eflicient results.

By my method of procedure above described consisting in first withdrawing from the initial section of the sheet lifted from the vat 4 the full strength high-density liquor held by the sheet and separately collecting the filtrate so obtained, without permitting any dilution, then washing out the weaker liquor acquired by the sheet from the weak liquor shower, and finally permitting the overflow of recovered weak liquor to be added to the recovery of lull-strength liquor. raises the density of the black liquor to a much highi gree than that of the black liquor recover the preceding process of procedure.

I claim:

1. In an apparatus of the character desi including a pulp digester and a vat into the discharge from the digester is receive combination of a rotary vacuum filter rota said vat, the interior of said filter being (1 into an endless series of consecutive con ments for receiving the liquor abstracted fro sheet of pulp picked up by the filter from th a vacuum chamber arranged to cover the partments located in a zone of predeter length through which zone the rising side filter travels, whereby the compartments i: zone and said vacuum chamber will recei liquor abstracted by the filter from the section of the sheet, means for separately c ing the liquor received from said vacuum i her, a second vacuum chamber arranged to the compartments located in a second zone 1 determined length through which the filter i after leaving the first zone during its con rotation, means for applying a shower of liquor to said sheet while the filter travels ti said first zone, said shower located a pre mined distance from the boundary betwee first and second zones to prevent the weak from said shower from penetrating e: through said sheet before entry into said 1 zone, means for applying a second shower 0 water to said sheet in said second zone, a 01 tion between said second vacuum chambi said means for applying said shower in sa: zone whereby the filtrate obtained from sa ond vacuum chamber will constitute the for said first-mentioned weak-liquor ShOWi means for separately collecting any exec trate from said second vacuum chamber is not used for said weak liquor shower am bining said excess with the filtrate obtaine said first zone, whereby a high density resulting mixture is obtained.

2. In the described process for the reco chemicals from digester pulp through the n of a rotary vacuum filter, the improvement consists in withdrawing the filtrate frc sheet of pulp in a first area without diluti separately collecting such filtrate, withd filtrate from the sheet of pulp in a scout located after said first area in the direc rotation of said filter, applying a weak shower to the pulp sheet in said first an predetermined distance from the bound: tween the first and second areas in order vent penetration of the weak liquor throi pulp sheet before entry of the pulp she the second area, applying a second shc wash water in said second area, using the obtained in said second area for said weal shower, and combining any excess of filtr stracted in the said second area and m for said weak liquor shower with the withdrawn from said first area, whereby density in the resulting filtrate mixture tained.

NORMAN A. LEWTHW! 

